This invention relates to an improved cracking catalyst. More particularly, this invention relates to a composite of a zeolite-containing cracking catalyst and a fluorided reforming catalyst.
Cracking reactions are used to convert heavier hydrocarbons into products having a lower average molecular weight useful in the production of motor fuels. Cracked products generally have a lower octane number than that desired for gasoline blending components. Catalytic reforming is a process which increases the octane number of cracked products by converting low octane hydrocarbons, such as paraffins and naphthenes, into aromatic-rich products. To minimize further processing, such as catalytic reforming operations, it is desirable that the gasoline components of the products of the cracking operation have as high an octane number as possible.
It is known in the art that catalytic activity of solid contact catalysts may be enhanced by incorporating into the catalyst acid activators, such as fluorine, as reported by Choudhary, Ind. Eng. Chem., Prod. Res. Div., 16, 12 (1977). Prior to the advent of zeolite cracking catalysts, amorphous-type catalysts, for example, alumina and silica-alumina catalysts, were enhanced by treatment with various fluorine compounds under anhydrous or aqueous conditions. For example, U.S. Pat. Nos. 2,336,165 (Connolly), 2,483,131 (Garrison), 2,694,674 (Starr et al.), and 2,848,380 (Thomas) all describe the preparation of improved alumina and silica-alumina cracking catalysts by treatment with various fluorine compounds.
More recent patents disclose fluorided reforming and dual-function catalysts. Some of these catalysts contain a zeolite component. For example, U.S. Pat. No. 4,191,638 (Plank et al.) describes a reforming catalyst which comprises a mixture of a zeolite and a conventional reforming catalyst, such as a metallic reforming catalyst. Both the zeolite component and the metallic reforming catalyst contain a halogen component, such as chloride or fluoride.
U.S. Pat. No. 3,702,312 (Wilson) discloses a dual-function catalyst comprising a fluorided zeolite and a hydrogenative metal component prepared by a sequence of steps to incorporate fluorine into the crystalline structure of the zeolite. Attempts to fluoride crystalline alumino-silicate by conventional halide impregnation with an aqueous solution of hydrogen fluoride destroyed the crystalline structure of the zeolite.
U.S. Pat. Nos. 4,097,368 (Hayes) and 4,098,679 (Hayes) describe dual-function composite catalysts comprising a combination of three or four metals on a porous carrier which may comprise a zeolite. Halogen may be added to the carrier material in any suitable manner, for example, by treatment of the carrier material with an aqueous solution of hydrogen fluoride.
The present invention relates to a fluorided cracking catalyst comprising a physical mixture of a fluorided reforming catalyst and a zeolite-containing cracking catalyst. The improved cracking catalyst of the present invention is prepared by treating a metallic reforming catalyst with an aqueous solution containing a fluorine compound, and then physically mixing the fluorided reforming catalyst with a zeolite-containing cracking catalyst. Use of the catalyst of this invention in cracking reactions yields higher octane products than can be obtained with conventional cracking catalyst.